Selective light-blocking optical products having a neutral reflection

ABSTRACT

Optical products that include a composite coating, deposited on a substrate, provided with at least one bilayer having a first layer and a second layer, each provided with a binding group component which together form a complementary binding group pair. The at least one bilayer comprises a pigment blend that includes: a) at least two pigments that, when mixed together and formed into a bilayer, exhibit a color reflection value that is less than about 2.5; and b) one or more pigments that when mixed and formed into a bilayer selectively block visible light in a wavelength range of interest.

FIELD OF THE INVENTION

The present invention broadly relates to optical products for use, for example, in automotive and architectural window applications. More particularly, the invention relates to optical products that provide selective light blocking while maintaining a desired neutral reflection.

BACKGROUND OF THE INVENTION

Light and energy blocking and color correction have typically been imparted to optical products such as solar control films by use of organic dyes. More particularly, current commercial practice for producing dyed film from polyester includes swelling of the molecular structure of the polyester in baths of hot organic solvent such as ethylene glycol during the dyeing process, as swelled polyester (particularly PET) films are capable of absorbing organic dyes. These films and their manufacturing processes suffer many drawbacks. For example, only a limited number of organic dyes are soluble and stable in the hot solvent swelling media used in the dyeing process and many of those are subject to degradation by high energy radiation (sub-400 nm wavelength) to which the substrate is subjected when used in window film applications, thereby shortening the useful lifetime of the product. Further, the dye typically permeates the entire thickness of the film such that there is no way to separate the filtration or blocking function of the film from its visible reflection, that is, from its external appearance.

To address some of these drawbacks, some film manufacturers have transitioned to using a pigmented layer on the surface of a base polymeric film for tinting a polymeric film. For example, U.S. Published Application number 2005/0019550A1 describes color-stable, pigmented optical bodies comprising a single or multiple layer core having at least one layer of an oriented thermoplastic polymer material having dispersed within it a particulate pigment. Such products can suffer a myriad of processing and performance drawbacks. For example, layers of this type are typically applied as thin films and require a relatively high pigment concentration to achieve a desired tint level, particularly in automotive window films with a relatively high desired level of darkening. These high pigment concentrations are difficult to uniformly disperse within the thin layer. And again, it may be difficult to separate the desired blocking properties of the product from its external appearance or reflection since the pigment is dispersed throughout the thickness of the thermoplastic polymer material.

More recently, layer-by-layer films have been developed to provide similar functionalities. Processes of making these films take advantage of charge-charge, hydrogen bonding, or other complementary interactions to assemble successive layers. This requires the use of solvents, typically water, to ionize molecules or support hydrogen donation and acceptance in the deposition solutions.

For example, U.S. Pat. Nos. 9,453,949 and 9,891,357, assigned to the assignee of the present application, the disclosures of which are incorporated herein by reference, disclose layer-by-layer composite films that include electromagnetic energy-absorbing insoluble particles that may be selected to provide pigmentation, UV-absorption, and/or IR-absorption properties. Likewise, U.S. Pat. No. 9,395,475, the disclosure of which is incorporated herein by reference, discloses layer-by-layer integrated stacks that serve as optical filters.

Optical products are known that can selectively block certain wavelengths of light, for example blue light that is believed to contribute to macular degeneration, cataracts, and the like. For example, shooting glasses having lenses containing yellow dyes are known to block blue light, but have a clearly discernible yellow tint to both the user and the observer. U.S. Pat. No. 8,882,267 discloses ophthalmic and nonophthalmic systems that are said to provide an average transmission of 80% or better transmission of visible light, to inhibit selective wavelengths of blue light, to allow for the wearer's proper color vision performance, and to provide a mostly color neutral appearance to an observer looking at the wearer wearing such a lens. The systems are said to be color balanced such that the yellow or amber color, or other unwanted effect of blue blocking is reduced, offset, neutralized or otherwise compensated for, so as to produce a cosmetically acceptable result, without at the same time reducing the effectiveness of the blue blocking.

A continuing need exists in the art for electromagnetic energy-absorbing optical products, and especially window films, that selectively filter bands of energy from transmitted visible light, producing a distinct transmitted color, while remaining relatively neutral in reflected color.

SUMMARY OF THE INVENTION

In one aspect, the invention relates to optical products that comprise a composite coating, deposited on a substrate, that includes at least one bilayer having a first layer and a second layer, each provided with a binding group component which together form a complementary binding group pair. The at least one bilayer comprises a pigment blend that includes: a) at least two pigments that, when mixed together and formed into a bilayer, exhibit a color reflection value that is less than about 2.5; and b) one or more pigments that when mixed and formed into a bilayer selectively block visible light in a wavelength range of interest. The resulting optical product selectively blocks visible light in the wavelength range of interest, while exhibiting a color reflection value that is less than about 2.5, as defined elsewhere herein.

In various aspects, the wavelength range of interest may be a 75 nm wavelength range, or a 50 nm wavelength range, or may be a wavelength range from 400 nm to 450 nm, or from 600 nm to 650 nm, or from 500 nm to 600 nm, or from 525 nm to 575 nm, or as described elsewhere herein.

In one aspect, the at least one bilayer of the optical products of the invention may comprise at least 3 bilayers, or as described elsewhere herein. In other aspects, the color reflection value of the optical products of the invention may be less than about 2.0, or less than about 1.5, or as described elsewhere herein.

In other aspects, the optical products of the invention may block at least 70% of visible light within the wavelength range of interest, or at least 80% of visible light within the wavelength range of interest, or as described elsewhere herein.

In one aspect, the optical products of the invention may comprise as a substrate a polyethylene terephthalate film. In another aspect, the composite coatings of the optical products of the invention may have a total thickness of 5 nm to 1000 nm, or as described elsewhere herein.

In other aspects, the optical products of the invention may be in the form of a window film that is applied to a vehicle, for example an automobile, an aircraft, or a boat. In another aspect, the optical products of the invention may be a composite interlayer for laminated glass.

In one aspect, the optical products of the invention may have a visible light transmission of no less than 40%, or no less than 60%.

Further aspects of the invention are as disclosed and claimed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in further detail below, and with reference to the accompanying drawings, wherein like reference numerals throughout the figures denote like elements and wherein:

FIG. 1 is a plot of the percent of light absorbed over the visible wavelength range of thin films made from five pigments that are useful according to the invention.

FIG. 2 is a plot of the percent of light reflected over the visible wavelength range of thin films made from five pigments that are useful according to the invention.

FIG. 3 is a plot of the percent of light reflected over the visible wavelength range of a thin film made from a blend of three pigments that is relatively neutral in reflectance across the visible spectrum.

FIG. 4 is a plot of the amount of light reflected along the visible spectrum for 2, 4, 6, and 8 layers of a yellow pigment useful according to the invention.

FIG. 5 is a schematic drawing that depicts a window film that is one embodiment of the present invention

FIG. 6 is a plot of the percent reflectance of wavelengths along the visible spectrum for two films prepared in the examples.

FIG. 7 is a plot of the percent transmittance of wavelengths along the visible spectrum for two films prepared in the examples.

DETAILED DESCRIPTION

According to the invention, optical products are provided that selectively block visible light in a wavelength range of interest, producing a distinct transmitted color, while remaining relatively neutral in reflected color. This is distinguished from light-filtering optical products in which residual color from a light-filtering functionality provided in the optical product results in a non-neutral reflection, that is, a reflection that is perceived by the eye as being colored.

In one aspect, then, the invention relates to pigmented optical products that selectively block visible light in a wavelength range of interest, for example a 50 nm wavelength range, while exhibiting a color reflection value, as defined herein, that is less than about 2.5.

In another aspect, the optical products of the invention block at least about 70% of visible light in a wavelength range of interest, while exhibiting a color reflection value, as defined herein, that is less than about 2.5.

According to the invention, optical products are provided that comprise composite coatings, deposited on a substrate, for example a polymeric substrate. These composite coatings comprise multiple bilayers that include a first layer and a second layer, each provided with a binding group component which together form a complementary binding group pair.

In one aspect, the invention relates to optical products that comprise a composite coating deposited on a substrate, in which the composite coating comprises at least one bilayer that includes a first layer and a second layer, each provided with a binding group component which together form a complementary binding group pair. In this aspect, the at least one bilayer comprises a pigment blend that includes: a) at least two pigments that when mixed together and formed into a bilayer exhibit a color reflection value that is less than about 2.5; and b) one or more pigments that, when formed into a bilayer, selectively block visible light in a wavelength range of interest, wherein the resulting optical product selectively blocks visible light in the wavelength range of interest, while exhibiting a color reflection value that is less than about 2.5.

When we say that the optical product or film, or an individual bilayer or plurality of bilayers, selectively blocks visible light within a wavelength range of interest, or within a defined wavelength range, or a predetermined wavelength range, we mean that the amount of light blocked within that wavelength range is greater than the amount of light blocked at other wavelength ranges of the same width within the visible light spectrum, which is defined herein for purposes of the invention as being from 400 nm to 700 nm. When we say that the light is selectively blocked, the definition of “blocked” is intended to encompass the light absorbed and the light reflected, as well as any light within the wavelength range that is scattered by the optical product; that is, all light that is not transmitted through the film or optical product so that it can be measured is considered to be “blocked,” whether the light blocked is absorbed, reflected, or scattered. The wavelength of interest can, of course, be predetermined, and a pigment selected, for example, that absorbs light within that preselected or predetermined wavelength range. Conversely, the wavelength range of interest may be randomly selected, in the sense that pigments may be tried for novelty or esthetic effect and chosen based solely on appearance and their effect on transmitted color, so long as the desired relatively neutral reflection is also achieved, as defined by the color reflection value.

We note that generally-accepted definitions of the wavelength range of visible light, as well as the definitions of perceived colors and the wavelengths of light within which the colors are perceived, are somewhat approximate. Further, the range within the visible spectrum that light according to the invention is selectively blocked will be, in part, a function of the type of light-filtering functionality provided to the optical products of the invention, for example the nature of the pigment particle(s) themselves, as well as the part of the visible light spectrum that is intended to be blocked, since different “colors” are perceived over varying wavelength ranges of light. For example, light perceived as red may be broadly and somewhat arbitrarily defined as light having a wavelength range as broad as from about 620 nm to about 750 nm (that is, partly outside the visible spectrum although perceivable by some individuals), a wavelength range of about 130 nm. Further, certain definitions of blue color (and especially those in which violet is defined within a separate wavelength range) are defined as having a wavelength range as narrow as from about 450 nm to about 495 nm, while other definitions of blue-colored light extend from 400 nm to 500 nm. The wavelength ranges of interest that are selectively blocked according to the invention are thus a function of the area of the visible wavelength range that is blocked, as well as the fundamental properties of the pigment(s) used to selectively block the light, especially the absorptive properties, as well as any interference properties of the film that may be a function of the thickness of the individual first or second layers, or the two layers that together form a bilayer.

Thus, according to the invention, the wavelength ranges of visible light which the optical products of the invention selectively block may be, for example, as narrow as a 25 nm wavelength range, or may be a 30 nm wavelength range, or a 40 nm wavelength range, or a 50 nm wavelength range, or a 60 nm wavelength range, or a 75 nm wavelength range, or a 100 nm wavelength range. In a broad aspect, the defined wavelength range of interest is a range in which the amount of light selectively blocked is greater than the amount blocked in any other visible wavelength range of the same width, with the visible wavelength range of light as defined herein being from 400 nm to 700 nm. Thus, in one aspect, the amount of light within the wavelength range of interest that is selectively blocked may be defined with respect to other ranges of the same width, such that the amount of visible light blocked within the wavelength range of interest is greater than the amount of visible light blocked within any other range of the same width in the visible light spectrum.

Further, the amount of light selectively blocked within the wavelength range of interest may also be defined in absolute terms. That is, the amount of light blocked within the wavelength range of interest may be at least 25%, or at least 35%, or at least 50%, or may be even higher, if desired, for example at least 60%, or at least 70%, or at least 75%, or at least 80%.

In various aspects, the wavelength range of interest may be, for example, from 400 nm to 450 nm, or from 450 nm to 500 nm, or from 500 nm to 550 nm, or from 550 nm to 600 nm, or from 600 nm to 650 nm, or from 600 nm to 700 nm, or from 500 nm to 600 nm, or from 525 nm to 575 nm, or as defined elsewhere herein. While some of the wavelength ranges just cited are 50 nm wavelength ranges, other wavelength ranges may be selected, as described here and elsewhere herein.

Similarly, the overall amount of visible light transmitted, or T_(vis), may likewise vary widely. Thus, the T_(vis) of the optical products of the invention may be at least 20%, or at least 30%, or at least 50%, or at least 60%, or at least 75%, or at least 80%, or alternatively may be no more than 10%, or no more than 20%, or no more than 30%, or as defined elsewhere herein.

The light measurements, as used herein, are those determined using the 1976 CIE L*a*b* Color Space. CIE L*a*b* is an opponent color system based on the earlier (1942) system of Richard Hunter called L, a, b. In the CIE L*a*b* color space, the three coordinates represent: the lightness of the color (L*=0 yields black and L*=100 indicates diffuse white); its position between red and green (a*, negative values indicate green while positive values indicate red); and its position between yellow and blue (b*, negative values indicate blue and positive values indicate yellow).

As used herein, the color reflection value is calculated from the formula sqrt[(a*)²+(b*)²]. For example, the color reflection value of an optical product or a bilayer having a reflective a* value of 0.5 and a reflective b* value of −0.5 would be 0.71, which is relatively neutral, while an optical product having a reflective a* value of 1.5 and a reflective b* value of −1.5 would have a color reflection value of 2.1 which, while still relatively neutral, is less neutral than the optical product having a color reflection value of 0.71. Relatively neutral color reflection values according to the invention, whether those used to describe the finished optical products or the pigment or pigment blends that comprise individual bilayers or group of bilayers, are those that are less than about 5, or less than 4, or less than or equal to 3, and especially values that are less than about 2.5, or less than about 2, or less than or equal to 1.5. Thus, the lower the color reflection value, the more neutral is the perceived color. So far as we are aware, this color reflection value and the formula for determining it have not been used previously, although the values used to calculate this color reflection value are generally-accepted measured values using the 1976 CIE L*a*b* Color Space, that is the a* and b* values, and as a practical matter are probably the most common way of defining color that is in use today.

The color reflection value just described is thus used according to the invention to determine whether the optical products of the invention have a suitably neutral reflection. The measurement is also used herein to determine the suitability of the pigment or pigment blends used in individual bilayers or a plurality of bilayers of the same pigment composition. In this measurement, a bilayer or plurality of bilayers is formed from the pigment or pigments on a suitable substrate, as further described herein, and a measurement obtained.

According to various aspects of the invention, optical products are thus provided that comprise composite coatings, deposited on a substrate, for example a polymeric substrate. These composite coatings comprise at least one bilayer that includes a first layer and a second layer, each provided with a binding group component which together form a complementary binding group pair.

In one aspect, the present invention relates to optical products that comprise a composite coating deposited on a substrate, in which the composite coating comprises at least one bilayer that includes a first layer and a second layer, each provided with a binding group component which together form a complementary binding group pair, the at least one bilayer comprising a pigment blend. According to this aspect of the invention, the pigment blend includes: a) at least two pigments that when mixed together and formed into a bilayer exhibit a color reflection value that is less than about 2.5; and b) one or more pigments that, when formed into a bilayer, selectively block visible light in a wavelength range of interest. In this aspect, the resulting optical product selectively blocks visible light in the wavelength range of interest, while exhibiting a relatively low color reflection value. In contrast to a sandwiched or interleaved embodiment disclosed and claimed in a copending application filed herewith on the same date having common assignee, the disclosure of which is incorporated herein by reference in its entirety, in the present invention, the at least one bilayer is comprised of a pigment blend that is selected such that neutrality as well as the desired selective blocking of visible light in a wavelength range of interest is achievable in a single bilayer. In its simplest form, this embodiment may be achieved with a single bilayer, though a plurality of bilayers may be preferred in certain instances. The blending technique of this aspect of the invention is particularly useful in cases where it is desirable to add an “accent” or “blocking” pigment to an otherwise neutral optical product to affect the product's transmitted color but not its reflected color.

When determining whether a pigment or pigment blend is suitable for use according to this aspect of the invention, the at least two pigments that when mixed together and formed into a bilayer exhibit a color reflection value that is less than about 2.5 are mixed and formed into a bilayer on a suitable substrate and the color reflection value is determined. The measurement is thus taken, for purposes of determining whether a given pigment or pigment blend is suitable for use according to the invention, on an isolated bilayer or bilayers, and not as incorporated into the finished optical product.

Similarly, with respect to the one or more pigments that, when formed into a bilayer, selectively block visible light in a wavelength range of interest, a bilayer or plurality of bilayers is formed from the one or more pigments on a suitable substrate, and the ability of the bilayer(s) to selectively block visible light in a wavelength range of interest is measured. The measurement is thus taken, for purposes of determining whether a given pigment or pigment blend is suitable to selectively block visible light in a wavelength range of interest, on an isolated bilayer or bilayers, and not on the finished optical product. We note again, however, that the color reflection value of the finished optical product is also determined in the same way.

In various aspects, the present invention is thus directed to optical products comprising a polymeric substrate provided thereon with a composite pigment coating. The composite pigment coatings are comprised of at least a first layer and a second layer which together form a single bilayer, at least one of which layers comprises or includes a pigment or pigment blend. referably, the first layer is immediately adjacent the substrate and a second layer is immediately adjacent to the first layer which was applied to or deposited on the substrate. Each of the first and second layers together thus form a bilayer. One or more additional first and second layers may thus be used to form a plurality of bilayers. Each of these bilayers or the plurality of bilayers taken together may also be described herein as a bilayer system, a composite coating, or an LbL coating. As described, each of the bilayers can be the same or different.

According to the invention, the composite pigment coating comprises a layer-by-layer coating that includes one or more pigments. Each of the layers of a given bilayer may comprise a polyionic binder, an insoluble pigment particle, or both. Each layer of the bilayer(s) includes a binding group component with the binding group component of the first layer and the binding group component of the second layer constituting a complementary binding group pair. As used herein, the phrase “complementary binding group pair” means that binding interactions, such as electrostatic binding, hydrogen bonding, Van der Waals interactions, hydrophobic interactions, and/or chemically-induced covalent bonds are present between the binding group component of the first layer and the binding group component of the second layer of the composite coating. A “binding group component” is a chemical functionality that, in concert with a complementary binding group component, establishes one or more of the binding interactions described above. The components are complementary in the sense that binding interactions are created through their respective charges.

According to the invention, the binding group component may be provided, for example, through a polyionic binder or a pigment. That is, if a selected pigment is charged, for example, so that it can serve as a binding group component of a given layer of the bilayer system, then that pigment may be used alone to form a layer of the bilayer. If the pigment does not include a binding group component, then that pigment may be combined with a molecule having a binding group component, for example a polyionic binder, to form a bilayer. We note that not every bilayer of the bilayer system need include a pigment, but according to the invention, those bilayers that include a pigment may have either a charged pigment or an uncharged pigment, or both.

According to the invention, a layer of the composite pigment coating may thus include a polyionic binder, which is defined as a macromolecule containing a plurality of either positively- or negatively-charged moieties along the polymer. Polyionic binders with positive charges are known as polycationic binders while those with negative charges are termed polyanionic binders. Also, it will be understood by one of ordinary skill that some polyionic binders can function as either a polycationic binder or a polyanionic binder, depending on factors such as pH, and are known as amphoteric. The charged moieties of the polyionic binder constitute the “binding group component” of a given layer.

Suitable polycationic binder examples include poly(allylamine hydrochloride), linear or branched poly(ethyleneimine), poly(diallyldimethylammonium chloride), macromolecules termed polyquaterniums or polyquats and various copolymers thereof. Blends of polycationic binders are also contemplated by the present invention.

Suitable polyanionic binder examples include carboxylic acid-containing compounds such as poly(acrylic acid) and poly(methacrylic acid), as well as sulfonate-containing compounds such as poly(styrene sulfonate) and various copolymers thereof. Blends of polyanionic binders are also contemplated by the present invention. Polyionic binders of both polycationic and polyanionic types are generally known to those of ordinary skill in the art and are described, for example, in U.S. Published Patent Application number US20140079884 to Krogman et al, incorporated herein by reference. Examples of suitable polyanionic binders include polyacrylic acid (PAA), poly(styrene sulfonate) (PSS), poly(vinyl alcohol) or poly(vinylacetate) (PVA, PVAc), poly(vinyl sulfonic acid), carboxymethyl cellulose (CMC), polysilicic acid, poly(3,4-ethylenedioxythiophene) (PEDOT) and combinations thereof with other polymers (e.g. PEDOT:PSS), polysaccharides, and copolymers of the above mentioned. Other examples of suitable polyanionic binders include trimethoxysilane functionalized PAA or PAH or biological molecules such as DNA, RNA or proteins. Examples of suitable polycationic binders include poly(diallyldimethylammonium chloride) (PDAC), Chitosan, poly(allyl amine hydrochloride) (PAH), polysaccharides, proteins, linear poly(ethyleneimine) (LPEI), branched poly(ethyleneimine) BPEI and copolymers of the above-mentioned, and the like. Examples of polyionic binders that can function as either polyanionic binders or polycationic binders include amphoteric polymers such as proteins and copolymers of the above mentioned polycationic and polyanionic binders.

The concentration of the polyionic binder in the first layer may be selected based in part on the molecular weight of its charged repeat unit but will typically be between 0.1 mM-100 mM, more preferably between 0.5 mM and 50 mM, and most preferably between 1 and 20 mM based on the molecular weight of the charged repeat unit.

According to the invention, if the binding group component of a given layer includes a negatively-charged pigment, then the polyionic binder of a complementary layer will typically be a polycationic binder, such as polyallylamine hydrochloride. The polyionic binders will typically be soluble in water and the composition used to form the layer will be an aqueous solution of polyionic binder. In an embodiment wherein the polyionic binder is a polycation and the first layer is formed from an aqueous solution, the pH of the aqueous solution may be selected so that from 5 to 95%, preferably 25 to 75%, and more preferably approximately half of the ionizable groups are protonated. Other optional ingredients in the first layer include biocides or shelf-life stabilizers.

It will be understood that when the first layer of a bilayer comprises a polycationic binder, the second layer may comprise a polyanionic binder or a negatively-charged insoluble pigment particle, or both. Of course, additional functionality may be provided to the optical products of the invention in the composite pigment coating. For example, one or more of the layers will typically be provided with electromagnetic energy-absorbing insoluble pigment particles, which themselves may be charged particles. The phrase “electromagnetic energy-absorbing” means that the particle is purposefully selected as a component for the optical product for its preferential absorption at particular spectral wavelength(s) or wavelength ranges(s). The term “insoluble” is meant to reflect the fact that the particle does not substantially dissolve in the composition used to form a given layer and exists as a particle in the optical product structure. Of course, the term electromagnetic energy-absorbing insoluble particles encompasses pigments; however, insoluble particles such as UV absorbers or IR absorbers, or absorbers in various parts of the electromagnetic spectrum that do not necessarily exhibit color, are also within the term and may be provided according to the invention.

Pigments suitable for use according to the invention are preferably particulate pigments with an average particle diameter from about 5 to about 300 nanometers, or from 10 to 100 nanometers, often referred to in the art as nanoparticle pigments, although there is not necessarily an upper limit to the particle size in those cases where a larger particle size may perform well in the LbL processes useful according to the invention. In one aspect, the surface of the pigment includes the binding group component of a given layer. Suitable pigments are available commercially as colloidally-stable water dispersions from manufacturers such as Cabot, Clariant, DuPont, Dainippon and DeGussa. Particularly suitable pigments include those available from Cabot Corporation under the Cab-O-Jet® name, for example 250C (cyan), 265M (magenta), 270Y (yellow), 554B (blue), 1027R (red), or 352K (black). In order to be stable in water as a colloidal dispersion, the pigment particle surface is typically treated to impart ionizable character thereto and thereby provide the pigment with the desired binding group component on its surface. It will be understood that commercially available pigments are sold in various forms such as suspensions, dispersions and the like, and care should be taken to evaluate the commercial form of the pigment and modify it as/if necessary to ensure its compatibility and performance with the optical product components, particularly in the embodiment wherein the pigment surface also functions as the binding group component of the second layer.

Multiple pigments or pigment blends will be utilized to achieve the selective blocking of visible light with relatively neutral reflection, as already described. However, it will again be understood that, should multiple pigments be used, they should be carefully selected to ensure their compatibility and performance both with each other and with the optical product components. This is particularly relevant in the embodiment wherein the pigment surface also functions as the binding group component of the layer, as for example particulate pigments can exhibit different surface charge densities due to different chemical modifications that can impact compatibility.

One or more of the layers of the LbL composite pigment coating may further include a screening agent that promotes even and reproducible deposition of the layer via improved dispersion of the pigment or polyionic binder within the layer by increasing ionic strength and reducing interparticle electrostatic repulsion. Screening agents are known to those of ordinary skill in the art and are described for example in U.S. Published Patent Application number US20140079884 to Krogman et al. Examples of suitable screening agents include low molecular weight salts such as halide salts, sulfate salts, nitrate salts, phosphate salts, fluorophosphate salts, and the like. Examples of halide salts include chloride salts such as LiCl, NaCl, KCl, CaCl₂, MgCl₂, NH₄Cl and the like, bromide salts such as LiBr, NaBr, KBr, CaBr₂, MgBr₂, and the like, iodide salts such as LiI, NaI, KI, CaI₂, MgI₂, and the like, and fluoride salts such as, NaF, KF, and the like. Examples of sulfate salts include Li₂SO₄, Na₂SO₄, K₂SO₄, (NH₄)₂SO₄, MgSO₄, CoSO₄, CuSO₄, ZnSO₄, SrSO₄, Al₂(SO₄)₃, and Fe₂(SO₄)₃. Organic salts such as (CH₃)₃CCl, (C₂H₅)₃CCl, and the like are also suitable screening agents. Sodium chloride is typically a preferred screening agent based on ingredient cost. The presence and concentration level of a screening agent may allow for higher loadings of the pigment or the binder such as those that may be desired in optical products with a T_(vis) of no more than 50% and also may allow for customizable and carefully controllable loadings in order to achieve customizable and carefully controllable optical product T_(vis) levels.

Suitable screening agent concentrations can vary with salt identity and are also described for example in U.S. Pat. No. 9,387,505 to Krogman et al, incorporated herein by reference in its entirety. In some embodiments, the screening agent concentration can range between 1 mM and 1000 mM or between 10 mM and 100 mM or between 30 mM and 80 mM. In some embodiments the screening agent concentration is greater than 1 mM, 10 mM, 100 mM or 500 mM.

The layers of the composite pigment coating may also contain other ingredients such as biocides or shelf-life stabilizers.

As noted, the composite pigment coatings of the invention may comprise a plurality of bilayers that may be the same or different. For example, an optical product of the invention may include first and second bilayers, each with a first layer and a second layer. For embodiments with a plurality of bilayers, it will be appreciated that the binders or pigments for each of the layers of a bilayer may be independently selected and that the layers containing pigment, for example, will in combination provide an additive effect to the user of the optical product. This additive effect can be customized and carefully controlled in part by the concentration of the pigment particles in each of the layers used as dispersed through the presence of the screening agent. For example, pigmented layers will, in combination, provide approximately an additive effect on the user's visually perceived color, that is, on the transmission of the film. In embodiments in which a plurality of bilayers is provided that include pigments, the pigments for each of the layers may be of the same or similar composition and/or color such that the additive effect is to increase intensity or depth or darkness of the visually perceived transmission of the optical product or, stated another way, to reduce electromagnetic transmittance in the visible wavelength range (or T_(vis)).

In one embodiment, carbon black may be used as a pigment for at least one layer, for example a layer in which the reflection is intended to be relatively neutral as evidenced by its color reflection value. Similarly, blends of pigments such as those discussed herein may be used together to obtain a bilayer or plurality of bilayers having a relatively neutral reflection. Pigments such as those listed above can also be used alone or as blends to obtain a bilayer or a plurality of bilayers that selectively blocks visible light in a wavelength range of interest. In general, the additive effect of multiple bilayers to the user is a visually perceived darkened color, reducing electromagnetic transmittance in the visible wavelength range (or T_(vis)). As discussed above, the present invention may be useful in products wherein relatively high levels of darkening are desired. Accordingly, in one embodiment, the optical products of the present invention have a T_(vis) of no more than 50%, or no more than 70%.

FIG. 1 depicts the percent of light absorbed over the visible wavelength range of five different pigments formed into approximately 200 nm thin films comprised of five bilayers. Each of these pigments is suitable for use according to the invention to form a first or second layer of a bilayer, either alone or in combination. These pigments may be used, for example, in blends selected to achieve a bilayer having a relatively neutral reflection, as defined by its color reflection value. They may likewise be used alone or in blends to obtain a bilayer that selectively blocks light within a wavelength range of interest. They also may each be used together with at least two other pigments to obtain a blend that when formed into a bilayer both selectively blocks visible light in a wavelength range of interest, while at the same time achieving a relatively neutral reflection, as evidenced by a relatively low color reflection value.

It can be seen that each of the five pigments in FIG. 1 exhibits a unique absorption curve, as certain portions of the visible spectrum are absorbed more strongly than others. When selecting one or more pigments that when mixed selectively block visible light in a wavelength range of interest, absorption curves of this type may be used to help select the appropriate pigment or pigments. For example, in FIG. 1 it can be seen that the yellow pigment 270Y strongly absorbs in the wavelength range from 400 nm to 450 nm, making it a suitable pigment to block visible light within this wavelength range. Similarly, pigment 554B absorbs strongly in the wavelength range from 500 nm to 600 nm, making it a good choice to block visible light within this wavelength range.

FIG. 2 depicts the percent of light reflected over the visible wavelength range for the same thin films for which the absorbance is depicted in FIG. 1. It can be seen that each of the five pigments in FIG. 2 exhibits a colored reflection, as opposed to a neutral reflection, as certain portions of the visible spectrum are reflected more strongly than others. These measured reflective properties may be used as a starting point when creating a pigment blend with suitable reflectance properties. However, the reflectance properties of a given bilayer, or of the finished optical products of the invention, may also be, in part, a function of interference that may also be occurring. Therefore, a certain amount of routine experimentation may be helpful when creating a pigment blend to obtain a bilayer having the desired neutrality, or color reflection value. Those skilled in the art will be readily able to select suitable pigments or pigment blends for use according to the invention using the relevant absorption and reflectance curves.

In FIG. 3 we see that, when three of the five pigments of FIGS. 1 and 2 (yellow pigment 270Y, magenta pigment 265M, and cyan pigment 250C) are blended together in an approximate ratio of 1:1:1 by pigment mass and formed into a single layer, no single pigment is dominant, and the bulk reflection becomes relatively neutral (sqrt((a*)²+(b*)²)=0.8). This can be seen graphically, since the percent reflection across the visible spectrum is approximately the same. This is but one example of a pigment blend useful according to the invention to provide a pigment blend having a relatively neutral reflection, as evidenced by its color reflection value. We see that for a reasonably homogeneous blend of two or more pigments we demonstrate the power of this approach by blending an accent or blocking pigment, for example a yellow pigment, directly into a slurry of relatively neutral black pigment (containing cyan, magenta, and carbon black), the effect of which is adding a blocking or transmissive filtering effect, while minimizing the yellow reflectance as evidenced by the relatively low color reflection value of the finished optical product.

FIG. 4 depicts the amount of light reflected along the visible spectrum for 2, 4, 6, and 8 layers of a yellow pigment useful according to the invention. It can be seen that increasing the absorptive ability of a layer-by-layer stack by adding additional yellow layers will result in a yellow reflection from the surface of the composite. However, the reflectance seen may in part be a result of thin-film interference that is a function of the thickness of a given layer or layers. Shown here, incrementally increasing the thickness of a yellow film 2 bilayers at a time, we see the reflected color is not entirely consistent. Adding very thin layers of pigment, for example 2 or 4 bilayers, may serve to reduce this effective reflectance effect. If more layers are desired, minor changes in formulation, for example of the neutral pigment blend, may be helpful in obtaining an optical product that blocks visible light within a wavelength range of interest while obtaining a suitably neutral color reflection value.

Thus, the present invention relates to optical products such as window films that include a polymeric substrate, for example PET or PVB, provided with a composite pigment coating, comprising at least one, and preferably a plurality, of layer-by-layer (LbL) bilayers deposited on the protective coating, at least one of which layers is or has incorporated into it a pigment. Each of the layers, as described herein, can be understood to have two faces, a first face and a second face, for the purpose of describing adjacent layers that each of the layers may be in contact with. Similarly, the finished optical products of the invention likewise have a first face and a second face, and may in general be applied to an automobile window or architectural window, for example, in either direction. When measuring a given optical product to determine whether its properties fall within the scope of the claims, the measurements may be those taken from either direction, and in some aspects of the invention, similar measurements will be obtained from both faces, although in other embodiments the measurements may be satisfied only when measured from one direction, and not the other.

Referring now to FIG. 5, a schematic drawing which is not to scale, an optical product is depicted that is a window film 10. The window film 10 includes a polymeric substrate 15, for example PET, provided with a composite pigment coating 50. Although in its simplest aspect, the optical products of the invention may be a single bilayer, FIG. 5 depicts a plurality of layer-by-layer (LbL) bilayers 20, 20′, 20″ deposited on the protective coating, at least one of which layers is or has incorporated into it a pigment. Each of the bilayers 20, 20′, 20″ of the invention is further comprised of a first layer 25, 25′, 25″ and a second layer 30, 30′, 30″. When used as an exterior or interior window film, the substrate may additionally have provided on its bottom an adhesive 5 for adhering the substrate to a window.

Referring still to FIG. 5, each of the bilayers 20, 20′, 20″ comprises a pigment blend that includes: a) at least two pigments that when mixed together and formed into a bilayer exhibit a color reflection value that is less than about 2.5; and b) one or more pigments that, when formed into a bilayer, selectively block visible light in a wavelength range of interest. According to the invention, the resulting optical product selectively blocks visible light in the wavelength range of interest, while exhibiting a color reflection value that is less than about 2.5. This color reflection value may be satisfied when the measurement is taken of the window film from either direction, or from both directions.

As depicted in FIG. 5, each of the bilayers 20, 20′, and 20″, is comprised respectively of a first layer 25, 25′, and 25″, and a second layer 30, 30′, and 30″. According to the invention, either the first layer 25, 25′, 25″, or the second layer 30, 30′, 30″, or both the first and second layer of each bilayer 20, 20′, 20″, will include the pigment blend just described. It will be understood that in the simplest aspect, the invention comprises a single bilayer 20, although in practice more than one bilayer may typically be used. Similarly, there may be added, before or after any or each of these bilayers, further bilayers that may be the same or different than those just described, so long as the bilayer comprised of the pigment blend is present in the stated sequence, and the resulting optical product obtains the desired color reflectance value.

The optical products of the invention may thus be films that are typically applied to the interior or exterior surface of a window, and preferably the interior. As noted, these films will be understood to have two faces, as does each of the layers of which the films are comprised.

When used as an exterior or interior window film, the substrate may additionally have provided on its bottom a means for adhering the substrate to a window. The optical product may thus have an adhesive layer provided on the substrate. The adhesive layer can be comprised of any adhesive that is suitable for bonding the substrate to a window. When being bonded to a window, pressure sensitive adhesives are preferable, with an acrylic-based adhesive being particularly preferable. Loctite Duro-Tak 109A (available from Henkel) is an example of such an adhesive. The adhesive layer may also have a release liner attached thereto. The release liner advantageously provides a release effect against the sticky adhesive layer. The release liner in the depicted embodiment can comprise any polyethylene terephthalate (PET) film with a silicone release coating that can be peeled from the adhesive layer leaving the adhesive layer on the base substrate. Alternatively, the adhesive and release layers may comprise a clear distortion-free adhesive with a polypropylene liner.

The present invention typically includes a polymeric substrate, preferably a film formed from a thermoplastic such as a polyester and preferably polyethylene terephthalate (PET). Suitable PET films are commercially available, for example from DuPont Teijin Films under the names Melinex 454 or LJX 112. Other suitable thermoplastics for forming the polymeric substrate include, for example, polyvinyl butyral, polyacrylic, polyimides, polyamides such as nylons, and polyolefins such as polyethylenes, polypropylenes and the like. The polymeric substrate may include conventional additives such as UV-absorbers, stabilizers, fillers, lubricants and the like, blended therein or coated thereon. Preferably, the polymeric substrate is transparent, which generally connotes the ability to perceive visually an object, indicia, words or the like through it.

The polymeric substrate may in the broadest sense be any substrate known in the art as useful as an optical product component. A suitable polymeric substrate is typically a flexible thermoplastic polymeric film, more particularly a polyethylene terephthalate (PET) film of a thickness, for example, from about 10μ to about 400μ, or from 15μ to 300μ, or from 20μ to 250μ; or a polyvinyl butyral (PVB) film, preferably of a thickness from 0.01 to 1 mm, or from 0.05 to 0.5 mm, or from 0.1 mm to 0.45 mm, and more preferably a thickness of 15 to 30 mils. Because window films that employ dyes exhibit a variety of drawbacks, the polymeric substrate is preferably an undyed transparent polyethylene terephthalate film. The term “undyed” means that the raw film has no appreciable color, and is not intended to exclude the presence of additives such as UV blockers that are present in small amounts and not intended to affect the appearance of the film. The polymeric substrate may also be a flexible polyurethane or flexible poly(vinyl chloride) film or may be a flexible multilayer polymeric composite film such as a polyurethane-based multilayer composite film as described for example in U.S. Pat. No. 8,765,263, the disclosure of which is incorporated herein by reference.

The polymeric substrate may further include additives known in the art to impart desirable characteristics. Examples include ultraviolet (UV) absorbing materials such as benzotriazoles, hydroxybenzophenones or triazines. A useful polymeric substrate with a UV absorbing additive incorporated therein is described in U.S. Pat. No. 6,221,112, which is incorporated herein by reference.

In one embodiment, wherein the polymeric substrate is a flexible polymeric film such as PET, the optical product may be a window film. As well known in the art, conventional window films are designed and manufactured with levels of electromagnetic energy transmittance or reflectivity that are selected based on a variety of factors such as, for example, product end-use market applications, and the like. In some settings, the desired optical properties include maximum rejection (reflection) of infrared wavelengths with less attention being paid to the amount of visible light transmitted or reflected. In other applications, specific degrees of visible light transmittance must be attained to meet government regulations, for example, in auto windshields in which regulations may require that the T_(vis) be 70% or greater. According to the present invention, the optical products of the invention selectively block visible light in a wavelength range of interest, while exhibiting a relatively neutral color reflection.

The visible light transmission (VLT or T_(vis)) is the spectral transmission in which the effect of each wavelength across the visible spectrum is weighted according to the eye's sensitivity to that wavelength. That is, it is the amount of light that is “seen” to be transmitted through the window film/glass system. The lower the number, the less visible light transmitted. It may be calculated using CIE Standard Observer (CIE 1924 1931) and D65 Daylight. As noted, the optical products of the present disclosure may have a visible light transmission within a broad range of VLT values, depending on the desired transparency, for example less than about 1%; from about 2% to about 5%; from about 25% to about 50%; about 28.5% to about 47%; about 30% to about 45%; about 28.5%; about 47%; about 55%; up to about 70%; or up to about 75%, or up to about 90%, or as described elsewhere herein.

In other embodiments, the optical product of the present invention may have visible light transmittance (T_(vis) or VLT) of no more than 50%, or no more than 45% or no more than 40%. Such levels of visible light transmittance are often desired in window films with high levels of darkening for certain automotive end use applications such as sidelights.

In another embodiment, the optical product of the present invention has visible light transmittance or T_(vis) of from 80 to 85%. Such levels of visible light transmittance are often desired in window films with relatively moderate to low levels of darkening (typically also with infrared absorption) for (to the extent permitted by governmental regulation) certain automotive end use applications such as windscreens. In yet another embodiment, the optical product of the present invention has visible light transmittance or T_(vis) of no less than 85%, or no less than 88% or no less than 90%. Such levels of visible light transmittance are often desired in window films with low to minimal levels of darkening for certain architectural end use applications. These various levels of visible light transmission may be achieved according to the invention through a reduction in visible light transmission achieved by the composite pigment coating.

The window films may optionally include further layers or coatings, other than any protective coating layer and the composite pigment coating, that are known to those of ordinary skill in the window film art. Coatings, for example, may include adhesive layers, protective release liners, and the like, as described herein. Such layers or coatings may be components of the polymeric substrate. Further, the polymeric substrate may be a laminated or multilayer structure.

In another embodiment, the optical product is an interlayer for laminated glass. In this embodiment, the polymeric substrate is formed from or afterward bonded to a film-forming material known in the art for this purpose, including for example plasticized polyvinyl butyral (PVB), polyurethanes, polyvinyl chloride, polyvinylacetal, polyethylene, ethyl vinyl acetates and the like. A preferred film-forming material for the interlayer is a plasticized PVB such as that used in a commercially available product from Eastman Chemical Company, SAFLEX® PVB interlayer. In this embodiment, the composite coating may be formed on at least one surface of the polymeric substrate.

In an embodiment wherein the substrate is a flexible polymeric film such as PET, the optical product may be a composite interlayer for laminated glass including at least one safety film or interlayer. The safety film may be formed from film-forming materials known in the art for this purpose, including, for example, plasticized polyvinyl butyral (PVB), polyurethanes, polyvinyl chloride, polyvinylacetal, polyethylene, ethyl vinyl acetates and the like. The safety film may be a plasticized PVB film or interlayer commercially available from Eastman Chemical Company as SAFLEX® PVB interlayer. The composite interlayer may include two safety films or one film layer and one coating layer, such as a PVB coating, that encapsulate the polymeric substrate. Composite interlayers of this general type are known in the art and are described for example in U.S. Pat. Nos. 4,973,511 and 5,091,258, the contents of which are incorporated herein by reference.

The polymer substrates described herein may thus include one or more thermoplastic polymers. Examples of suitable thermoplastic polymers can include, but are not limited to, poly(vinyl acetal) resins (such as PVB), polyurethanes (“PU”), poly(ethylene-co-vinyl)acetates (“EVA”), polyvinyl chlorides (“PVC”), poly(vinyl chloride-co-methacrylate), polyethylene, polyolefins, ethylene acrylate ester copolymers, poly(ethylene-co-butyl acrylate), silicone elastomers, epoxy resins, and acid copolymers such as ethylene/carboxylic acid copolymers and ionomers thereof, derived from any of the previously-listed polymers, and combinations thereof. In some embodiments, the thermoplastic polymer can be selected from the group consisting of poly(vinyl acetal) resins, polyvinyl chloride, and polyurethanes, or the resin can comprise one or more poly(vinyl acetal) resins. Although some of the polymer layers may be described herein with respect to poly(vinyl acetal) resins, it should be understood that one or more of the above polymer resins and/or polymer layers including the polymer resins could be included with, or in the place of, the poly(vinyl acetal) resins described below in accordance with various embodiments of the present invention.

When the polymeric substrates described herein include poly(vinyl acetal) resins, the poly(vinyl acetal) resins can be formed according to any suitable method. Poly(vinyl acetal) resins can be formed by acetalization of polyvinyl alcohol with one or more aldehydes in the presence of an acid catalyst. The resulting resin can then be separated, stabilized, and dried according to known methods such as, for example, those described in U.S. Pat. Nos. 2,282,057 and 2,282,026, as well as Wade, B. 2016, Vinyl Acetal Polymers, Encyclopedia of Polymer Science and Technology. 1-22 (online, copyright 2016 John Wiley & Sons, Inc.). The resulting poly(vinyl acetal) resins may have a total percent acetalization of at least about 50, at least about 60, at least about 70, at least about 75, at least about 80, at least about 85 weight percent, measured according to ASTM D1396, unless otherwise noted. The total amount of aldehyde residues in a poly(vinyl acetal) resin can be collectively referred to as the acetal component, with the balance of the poly(vinyl acetal) resin being residual hydroxyl and residual acetate groups, which will be discussed in further detail below.

The polymeric substrates according to various embodiments of the present invention can further include at least one plasticizer. Depending on the specific composition of the resin or resins in a polymer layer, the plasticizer may be present in an amount of at least about 5, at least about 15, at least about 25, or at least about 35, or at least about 50, parts per hundred parts of resin (phr) and/or not more than about 120, not more than about 100, not more than about 90, not more than about 75, not more than about 70, or not more than about 55, not more than about 50, not more than about 45, or not more than about 40 phr, or in the range of from about 5 to about 120, about 10 to about 110, about 20 to about 90, or about 25 to about 75 phr.

As used herein, the term “parts per hundred parts of resin” or “phr” refers to the amount of plasticizer present as compared to one hundred parts of resin, on a weight basis. Further, when the plasticizer content of a polymer layer is provided herein, it is provided with reference to the amount of plasticizer in the mix or melt that was used to produce the polymer layer.

In another aspect, the present invention is directed to methods for forming optical products. In one embodiment, the method of the present invention includes applying to the protective layer a composite pigment coating. The composite pigment coating may be applied to the protective layer by applying a first layer to the protective layer and thereafter applying a second layer to form a bilayer. The process is then repeated until the desired number and nature of bilayers is achieved. The first layer of the bilayer may include a polyionic binder and/or a pigment, and the second layer may likewise include a binder and/or a pigment, with each of the first and second layers including a binding group component which together form a complementary binding group pair. At least one of the layers, and especially those layers that include a charged pigment particle, may include a screening agent as defined above.

In a preferred embodiment, at least one of the first and second layers are applied as an aqueous dispersion or solution and most preferably both of the first and second layers are an aqueous dispersion or solution. In this embodiment, both applying steps (a) and (b) are performed at ambient temperature and pressure.

The optical products of the present invention are thus preferably manufactured using known “layer-by-layer” (LbL) processes such as described in Langmuir, 2007, 23, 3137-3141 or in U.S. Pat. Nos. 8,234,998, 8,689,726 and 9,387,505, co-invented by co-inventor Krogman of the present application, the disclosures of which are incorporated herein by reference.

The following examples, while provided to illustrate with specificity and detail the many aspects and advantages of the present invention, are not be interpreted as in any way limiting its scope. Variations, modifications and adaptations which do depart of the spirit of the present invention will be readily appreciated by one of ordinary skill in the art.

The light measurements, as used herein, are calculated using the 1976 CIE L*a*b* Color Space convention, and were measured using a Perkin-Elmer Lambda 900 UV-Vis-NIR Spectrometer.

EXAMPLES

In the examples, we describe two techniques for constructing a film which absorbs 80% of blue light (between 400 and 450 nm), but only 60% in the remainder of the spectrum, and both of which create a material which is substantially neutral in reflection. Employing an interleaved structure (Ex. 1) of accent color layers and neutral black layers, or blending the accent color directly into the neutral slurry prior to deposition (Ex. 2), produce the same effects.

Example 1

To form the optical product of Example 1, which is being pursued in a separate patent application filed on the same day as the present application and has a common assignee herewith, the entire disclosure of which is incorporated herein by reference, a sheet of polyethylene terephthalate (PET) film (as substrate) with a thickness of 75 microns was pretreated as known in the art by passing through a conventional corona treatment. A first layer was then formed on the PET sheet by spray coating, at ambient pressure and temperature, a first coating composition of 20 mM solution, based on the molecular weight of the charged repeat unit, of polyallylamine hydrochloride with an adjusted pH of 9.5, as further described below. Excess non-absorbed material was rinsed away with a deionized water spray. A composition for use in forming the second layer was then sprayed onto the surface of the first layer with excess material again rinsed away in a similar fashion with the first layer and electromagnetic energy-absorbing particle-containing second layer constituting the composite color coating of the present invention.

In this example a first coating composition for the first layer of the optical product was formed by dissolving 0.94 g of poly(allylamine hydrochloride) per liter of deionized water, and titrating the pH of the resulting solution to 9.5 using sodium hydroxide. A neutral pigmented second coating composition for forming the second layer of a neutral composite layer, a 0.5 wt % solids pigment blend dispersion of 6.07 g Cab-o-Jet 352K black, 10.85 g Cab-o-Jet 250C cyan, and 15.05 g Cab-o-Jet 265M magenta pigments in 1 L of distilled water was also formed, with 2.92 g of sodium chloride added as screening agent to ionically screen the colloidal particles and prepare them for deposition. The 352K black pigment has ionizable carboxylate functionality at its surface while the 250C cyan pigment and 265M magenta pigment have ionizable sulfonate functionality at their respective surfaces. Titrating the second coating composition to pH 7.5 produces a scenario where approximately 75% of the Cab-o-Jet 352K black pigment ionizable carboxylate functionalities are ionized to form negative carboxylate groups, while 25% are not ionized and are present as carboxylic acids. This was found empirically to reduce the charge density on the black pigment to more closely match the sulfonate charge density on the cyan and magenta pigments. The above procedure may then be utilized to form an optical product with the first layer from the first composition above and a second layer formed from the pigment blend-containing second coating composition described above. This deposition process may be repeated for the substrate multiple times to deposit multiple composite coatings on the substrate and achieve increasing coloration with each repetition.

Similarly, another second coating composition for forming the second layer of an accent composite layer, a 0.5 wt % solids pigment dispersion of 35.0 g Cab-o-Jet 270Y yellow pigment in 1 L of distilled water, was also formed, with 2.92 g of sodium chloride added as screening agent to ionically screen the colloidal particles and prepare them for deposition. An optical product was created by repeating the above procedure seven times using the first coating composition and the neutral second coating composition, followed by three times using the first coating composition and the accent second coating composition, followed by two times using the first coating composition and the neutral second coating composition, thereby forming a coating which is PET/7 layers black/3 layers yellow/2 layers black. The reflection and transmission of this interleaved composite coating were then measured using a UV-vis spectrometer, the results of which are depicted graphically in FIGS. 6 and 7, respectively.

Example 2

Using the same first coating composition from Example 1, a second coating composition is created by mixing 4.25 g Cab-o-Jet 352K black, 6.60 g Cab-o-Jet 250C cyan, 9.77 g Cab-o-Jet 265M magenta, and 12.24 g Cab-o-Jet 270Y yellow pigments in 1 L of distilled water, with 2.92 g of sodium chloride added as screening agent to ionically screen the colloidal particles and prepare them for deposition. In this example, the 270Y yellow pigment is added as the accent or blocking color directly to the pigment blend of cyan, magenta, and carbon black. An optical product is then created by repeating the procedure of Example 1 twelve times using the first coating composition from Example 1 and the accented second coating composition. The reflection and transmission of the composite coating were then measured using a UV-vis spectrometer, the results of which are depicted graphically in FIGS. 6 and 7, respectively.

The transmission measurements of the two films of Examples 1 and 2 are quite similar because they contain the same quantities of absorptive pigments, even though the film architectures are quite different, and as such produce similar transmitted color. Notably, the reflection measurements are also very similar, which is surprising since the reflection in Ex. 1 was neutralized by creating an interleaved structure, whereas Example 2 comprises a blend of pigments.

TABLE 1 Example Transmission Reflection No. a* b* a* b* neutrality 1 −6.47082 14.86763 0.284662 −0.19185 0.34327505 2 −7.81767 15.93019 −0.49681 0.294908 0.57774645

Notably, as can be seen from Table 1, both coatings show the strongly positive b* value indicative of very yellow transmission, yet substantially neutral reflection with the color reflection value, sqrt[(a*)²+(b*)²], remaining very small.

A person skilled in the art will recognize that the measurements described herein are measurements based on publicly available standards and guidelines that can be obtained by a variety of different specific test methods. The test methods described represent only one available method to obtain each of the required measurements.

The foregoing description of various embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise embodiments disclosed. Numerous modifications or variations are possible in electromagnetic energy of the above teachings. The embodiments discussed were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled. 

We claim:
 1. An optical product comprising a composite coating, deposited on a substrate, that includes at least one bilayer having a first layer and a second layer, each provided with a binding group component which together form a complementary binding group pair, the at least one bilayer comprising a pigment blend that includes: a) at least two pigments that, when mixed together and formed into a bilayer, exhibit a color reflection value that is less than about 2.5; and b) one or more pigments that when mixed and formed into a bilayer selectively block visible light in a wavelength range of interest, wherein the resulting optical product selectively blocks visible light in the wavelength range of interest, while exhibiting a color reflection value that is less than about 2.5.
 2. The optical product of claim 1, wherein the wavelength range of interest is a 75 nm wavelength range.
 3. The optical product of claim 1, wherein the wavelength range of interest is a 50 nm wavelength range.
 4. The optical product of claim 1, wherein the wavelength range of interest is from 400 nm to 450 nm.
 5. The optical product of claim 1, wherein the wavelength range of interest is from 600 nm to 650 nm.
 6. The optical product of claim 1, wherein the wavelength range of interest is from 500 nm to 600 nm.
 7. The optical product of claim 1, wherein the wavelength range of interest is from 525 nm to 575 nm.
 8. The optical product of claim 1, wherein the at least one bilayer comprises at least 3 bilayers.
 9. The optical product of claim 1, wherein the color reflection value is less than about 2.0.
 10. The optical product of claim 1, wherein the color reflection value is less than about 1.5.
 11. The optical product of claim 1, wherein the optical product blocks at least 70% of visible light within the wavelength range of interest.
 12. The optical product of claim 1, wherein the optical product blocks at least 80% of visible light within the wavelength range of interest.
 13. The optical product of claim 1, wherein the substrate comprises a polyethylene terephthalate film.
 14. The optical product of claim 1, wherein the composite coating has a total thickness of 5 nm to 1000 nm.
 15. The optical product of claim 1, in the form of a window film that is applied to a vehicle.
 16. The optical product of claim 12, wherein the vehicle is an automobile, an aircraft, or a boat.
 17. The optical product of claim 2, wherein the optical product is a composite interlayer for laminated glass.
 18. The optical product of claim 16 wherein said optical product has a visible light transmission of no less than 40%.
 19. The optical product of claim 16, wherein said optical product has a visible light transmission of no less than 60%. 